1. Field of the Invention
The present invention relates to a method for manufacturing MOS transistors.
2. Discussion of the Related Art
MOS transistors have speed, power consumption, and power characteristics which depend, among others, on the gate insulator thickness. In many cases, three types of MOS transistors having different gate insulator thicknesses are desired to be formed on the same chip. For example, if the transistor should stand high voltages (in the general case of power transistors), the gate insulator thickness should be large. If the transistor should be the fastest possible, all its dimensions, and especially its gate insulator thickness, should be as small as possible, but this generally causes the existence of non-negligible leakage currents. It is thus desirable to form fast transistors with less loss. To achieve this, transistors having an intermediary gate insulator thickness may be selected.